It is highly desirable that packages for perishable liquid or dry foods, such as milk products, juices, and cereals, be moisture-, oxygen- and aroma-proof for improving the durability of the product. The traditional packaging procedure has been to provide a fiber-based packaging material which includes a grey aluminum foil to provide an efficient protection against the penetration of moisture and oxygen into and the escape of aromas from the packed product. However, the customary use of aluminum foil in fiber-based packaging applications is now decreasing due to its high costs, environmental hazards and regulations concerning the recycling of materials. Aluminum does not decompose in landfills, and it is difficult to regenerate packaging cardboard lined with aluminum.
The use of aluminum as an oxygen and aroma barrier in food packages has been replaced by polymers to an increasing extent, the most important polymers being ethyl vinyl alcohol copolymer (EVOH), polyamide (PA), and polyethylene terephthalate (PET). By combining these polymers with binding agents and heat sealing polymers, a multi-layer cardboard can be formed, which has gas barrier characteristics almost comparable with aluminum. A disadvantage of these materials is their permeability to water vapor, and, therefore, all these materials have an undesirable high Moisture Vapor Transition Rate (MVTR).
In order to overcome this disadvantage, the use of polyolefin layers as moisture barriers has been attempted, either alone or in combination with the above-mentioned polymers. Low Density Polyethylene (LDPE) is a widely used polyolefin used for this purpose. For even lower MVTR rates, LDPE layers may be combined with high density polyethylene layers (HDPE). A disadvantage of these laminates is high film thicknesses required to obtain the necessary barrier properties.
In view of increasing material costs and tightening environmental regulations, another trend has been to decrease the amount of polymer used in coating packaging cardboard.
In view of the foregoing disadvantages associated with the prior art laminates and packaging materials, there remains a need for packaging materials that are characterized by improved barrier properties and that are environmentally friendly and inexpensive to manufacture.